As is well known, a typical system for furnishing water to a hydroelectric plant or any other facility requiring processed water may involve an auxiliary watercourse such as a canal alongside a main or natural stream such as a river. Water from the main stream is diverted to the canal which has an outlet leading to the generating or like plant. The recognized problem is that fish and debris from the main stream also enter the canal and, unless filtered out or otherwise directed away from the plant intake, enter that intake with attendant disadvantages.
Many efforts have been made to solve the problems, such as providing louvers across the stream, but the fish and debris pass through the louvers. If the louvers are more closely spaced apart, the fish impinge thereon and are injured or killed, besides which the pressure drop across the louvers becomes intolerable. Other systems use reciprocating or other types of movable screens, which are costly and inefficient and incur relatively high rates of fish mortality.
According to the present invention, an improved system is employed in an elongated watercourse having bottom and opposite side walls defining a channel or canal having an inlet for taking water from a main stream and having an outlet for leading water to the intake of a generating or like plant. The improved system effectively screens out fish and debris from the plant intake with little if any harm to the fish, which are directed to one or more exits separate from the canal outlet and plant intake and led back to the main stream. The arrangement includes a plurality of pairs of upright screens rising from the watercourse or canal bottom to at least the water level in the watercourse. The screens in each pair are arranged in convergent fashion to form a tapering channel having its large end upstream in the canal and its smaller end downstream. The smaller end leads to an exit apart from the canal outlet. The pairs of screens are interconnected at their free upstream ends so that when viewed from above, the whole results in a zigzag screen pattern spanning the canal from one side wall to the other. The angle between adjacent screens of each pair is relatively small so as to increase total screen area and to direct the fish toward the associated exit with little if any impingement of the fish on the screens. The major volume of water of course passes through the screens and flows via the canal outlet to the plant intake.
A further feature of the invention is a system for cleaning the screens periodically to dislodge accumulated debris. The cleaning means employs water-pressure-operated rotary spray means arranged to direct clean water against the inner or water-facing sides of the screens in backwash fashion, and the dislodged debris flows out the exits to the main stream.
Further features and objects of the invention will become apparent from the ensuring description of a preferred embodiment of the invention, taken with the accompanying drawings.